Field of the Invention
The present invention relates to an auxiliary power unit for use with a motor vehicle which provides power sources for one or more electrical devices using a cigarette lighter socket mounted on the vehicle.
Recently, electrical devices such as portable television sets and compact disk (CD) players have been frequently used in motor vehicles. Power for operating these electrical devices is, typically, obtained through a cigarette lighter socket mounted in a dash board of the motor vehicle. However, because motor vehicles generally have only one cigarette lighter socket, an auxiliary power unit must be employed to provide power for operating more than one such electrical device.
Generally, such an auxiliary power unit comprises a plug which connects to the cigarette lighter socket, and a plurality of branch sockets electrically connected to the plug. Further, current fuses and temperature fuses are typically provided at each of the branch sockets to prevent the flow of excess current to the sockets and to prevent the sockets from reaching extreme temperatures.
The auxiliary power unit thus constructed, however, suffers from various drawbacks. For instance, when one or more of the current fuses or temperature fuses blows, it must be replaced, thereby requiring maintenance by either the motor vehicle operator or service personnel. Further, because a plurality of electrical devices are often connected to the auxiliary power unit, the total interrupting capacities of the current fuses is relatively large. Hence, the main fuse connected between the auxiliary power unit and the vehicle battery may blow before the current fuses blow. In such a case, maintenance of the blown fuse(s) is even more troublesome.